Don't think it's "hooker math."  I think (actually hope) she is cleverly differentiating between local and touring clientele. A provider's local business is built with a reputation for consistent, attractive pricing and services. In other words, connection with regulars.
Conversely, touring business is predicated on clients jumping at brief opportunities for novelty.  
So it's perfectly possible that in Mona's $350 deal we are looking at another little bit of genius, along the lines of the pricing of several of Minnesota's most famous and popular women, e.g. HM, JS... whose 90 minute sessions are amongst the best deals in the industry.  No names because it's not a Friday. Actually just checked and HM's rates are a little higher now than I remember. But then she has already established her magic. She is the holy grail.

P.S. Many of us probably routinely pass by locals in favor of travelers when the prices are equal. Why? Because the traveler will be gone tomorrow and that puts pressure on the decision. Nevertheless I am always looking for the holy grail, and the number one quality of that grail is authentic chemistry during the encounter, leading to a goodbye that makes me want to do it again very soon.  Meaning that I really want the grail, the ATF, to be local.